Introduction: In addition to the a and [unreadable] defensins produced by human leukocytes and epithelial cells, many nonhuman primates produce ?-defensins, representing a third defensin subfamily. ?-defensins lack potent antibacterial or antifungal activity, but have broad antiviral properties. Retrocyclins are ?-defensins whose structures are based on the sequences of expressed (but untranslated) human ?-defensin pseudogenes. Broad, Long term objectives: To use retrocyclins to enhance pulmonary defenses to viral aerosols. Specific aims. 1. To test retrocyclins against potential viral bioterrorism agents, including Influenza A and B (Orthomyxoviridae), HPIV3 (Paramyxoviridae), West Nile and Yellow Fever virus (Flaviviridae) SARS-CoV (Coronaviridae), Vaccinia (Poxviridae), VEE, an alphavirus (Togaviridae), and Tacaribe virus (Arenaviridae) 2. To examine the interactions of retrocyclins with surfactant proteins SP-A and SP-D. 3. To test the effects actions of RC2 on monolayers and bilayers of pulmonary surfactant phospholipids. Research Design. Retrocyclin-2 (RC-2) and selected analogs will be prepared by solid phase peptide synthesis. Viruses will be tested in vitro by standard plaque reduction and CPE reduction assays. The effects of retrocyclins on the integrity of surfactant phospholipid films will be tested in monolayer systems by using a Langmuir-Blodgett trough, and in bilayer systems by using vesicles composed of surfactant lipids and associated surfactant proteins SP-B and SP-C. Binding of retrocyclins to SP-A and SP-D will be studied by surface plasmon resonance. Effects of retrocyclins on the intrinsic antiviral activity of SP-A and SP-D (and vice versa) will be studied using proteins purified from abattoir-obtained porcine lungs in standard plaque reduction and CPE reduction assays. Health relatedness and Agency Mission. This application is in direct response to PA 04-119. Lay language summary. Many natural viral infections begin with exposure to air that contains viruses. Viral aerosols may also allow bioterrorists to deliver incapacitating viruses. We propose to test the activity of retrocyclins (newly discovered antiviral peptides) against potential viral bioterrorism agents, and to determine their biocompatability with ELF-the thin fluid layer that covers the surface of the pulmonary air sacs. [unreadable] [unreadable]